In recent years, handheld terminal devices such as laptop computers, cellular phones and PDA (personal digital assistant) are being remarkably spread. As a secondary battery used as a power source for these handheld terminal devices, e.g., a nickel-metal hydride secondary battery and a lithium ion secondary battery are often used. The handheld terminal devices are required to have a comfortable portability, and therefore such devices are rapidly becoming more compact, thin and lightweight with better performance. As a result, the handheld terminal devices are now being used in a wide variety of situations. Like the handheld terminal devices, the secondary battery is also required to be more compact, thin and lightweight with better performance.
For improving the performance of the secondary battery, there have been studied modification of the electrode, the electrolytic solution, and other members of the battery. Among them, the electrode is usually produced by mixing an electrode active material and, if necessary, a conducting agent such as electroconductive carbon, with a binder composition in which a polymer serving as a binder is dispersed or dissolved in a solvent such as water or an organic liquid to prepare a slurry, then applying the slurry onto a collector, and drying the slurry. As to electrodes, in addition to the studies on the electrode active material and the collector themselves, there have also been made studies on the polymer serving as the binder for effecting binding of, e.g., the electrode active material to the collector. For example, Patent Literatures 1 and 2 describe techniques about binders for secondary batteries.